This invention relates to profile control techniques for subterranean formations; and more particularly this invention relates to methods of selectively establishing a barrier to fluid flow within subterranean formations.
The principal strategies of oil recovery processes focus on recovering the greatest amount of oil with minimal loss of advancing oil or flooding fluids to thief zones or played out zones, and with minimal production of connate water.
In the drilling and production of fluid mineral deposits such as petroleum oil and gas from subterranean reservoirs, the presence of connate water (usually in the form of an aqueous brine solution) is a continuing problem. In almost every subterranean formation wherein either petroleum oil or gas is present in quantities which make production practical, water is also found to be present. Usually, certain portions or strata of an oil bearing formation may be considered oil-rich; and other portions or strata of the formation may be considered water-rich.
Production of connate water along with oil or gas from a producing formation is not desired for many reasons, among them being the extra production expenses encountered, the necessity for separating the oil and water following production, and the extra concern in disposing the undesired brackish water which is a pollutant to the surrounding terrain.
Another problem associated with oil recovery processes is the existence of played out zones. After an oil bearing formation has been worked for a time, some of the oil rich strata will have been depleted of recoverable oil or "played out". In subsequent production processes it is uneconomical and inefficient to continue expending production fluids to these played out zones. Such played out zones have little oil available for production and because of their initial accessibility for oil production these played out preferentially consume subsequently injected production fluid to the exclusion of the remaining oil bearing strata.
The presence of water rich strata and played out areas is especially critical in those instances wherein a post primary recovery process is employed which utilizes a liquid flooding medium such as water (e.g. a waterflood operation) that is injected into the formation as through an injection well. By the very nature of such processes, a relatively large amount of injected water will be produced at the producing well or wells. The focus of the problem in such situations is to avoid or plug the water rich strata and played out areas in an effort to prevent thief of the advancing oil and flooding compositions by water rich strata or played out zones and to maintain a high oil to water ratio of fluids recovered from the formation.
The problem as set forth above and the many disadvantages encountered have been recognized by the oil and gas production industry for many years. Many efforts have been made to solve the problem in whole or in part to yield production at a more favorable oil-to-water production ratio and to provide for more complete recovery of available oil in subsequent waterflooding, steam injection, and surfactant flooding operations.
One prior art attempt at solution of the problem has been to use various solvents to selectively or preferentially plug water-rich portions or create barriers to water flow.
Applicant himself has proposed various solutions. See, for example, Applicant's prior art U.S. Pat. Nos. 3,749,174 issued July 31, 1973; 3,811,508 issued May 21, 1974; 3,865,189 issued Feb. 11, 1975; 3,866,684 issued Feb. 18, 1975; 3,866,685 also issued Feb. 18, 1975; 3,876,438 issued, Apr. 8, 1975; and 4,328,864 issued May 11, 1982.
Many of the prior art methods have been at least partially successful, and have afforded at least partial solution to the problem in certain instances and under certain well conditions. Nevertheless, the problem mentioned above still plagues the industry and remains critical. Indeed, with the rapid increase in production costs and the enforcement of pollution regulations by various governmental agencies, the industry is in very great need for a practical and inexpensive solution to this long-felt problem.
One of the primary difficulties with the prior art solutions is their impracticality for use in most situations because of the expense involved. It must be remembered in connection with the methods of this type that, typically, huge volumes of materials must be injected into the formations. Since the oil or gas which is produced is of limited value to begin with, and since production expenses are already high, any material injected into the well for selective plugging or for any other reason must, to be at all practical, be quite inexpensive. Most of the methods of the prior art known to Applicant entail the use of materials which are much too expensive to use in large volumes, in the typical situation encountered by the driller or operator.
Another major difficulty faced by the industry, is the inability to place a plug or create a horizontal or vertical barrier to fluid flow at some desired distance remote from but somewhat concentric to a wellbore. For example, to correct a steam override problem it would be desirable to establish a fluid flow barrier around a producing wellbore but at some distance remote from the wellbore. Such a barrier would then deflect uprising steam from dissipating into an upper played out zone and direct the steam through a lower producing zone to the production well. Heretofore, there has been no inexpensive or selective mechanism to establish a flow barrier along the length of a borehole or some portion thereof, but remote from it.